With a large, 34-car field on the relatively small, 1.5 mile track, drivers had said before the race that they were worried about what would happen if something went wrong as they tore around the oval at speeds topping 220 mph, Quinn said.

"No normal human being really has the reaction time to avoid anything" if cars started to collide at those speeds on a track that small, he added. Compare the field and track to this year's Indianapolis 500, which Wheldon won: in that race, there were 33 cars on a 2.5 mile oval — meaning there was much more room to spread out and avoid trouble.

"It's unfortunate that early on in the race they've got to be racing so close. ...," Team Penske owner Roger Penske said afterward, according to The Associated Press. "You always worry about those at these mile-and-a-halves at the speed and with this many cars."

So why had the IndyCar series packed that many cars on the Vegas speedway? Race organizers "wanted to make it a real spectacle," Quinn said, with lots of tight passing at high speeds.

Adding to the drama: If Wheldon had won the race, he would have shared in a special $5 million prize. The prize, to be split with his race team and a fan selected at random, had been offered to any non-IndyCar series driver who won the race. Wheldon was the only such driver in the race.

In the end, after the horrific crash in lap 11, the race was canceled.

As the Las Vegas Review-Journal reports, "the crash started when Wade Cunning­ham's car swerved in Turn 2 and [J.R.] Hilde­brand inadvertently drove his car over the rear of Cunningham's. That sent Hilde­brand's car airborne, before it darted to the right and into the guardwall. The suddenness of the contact created a chain reaction with 13 other cars — all racing at about 220 mph — caught up in the wreck. A few spun in front of Wheldon and his car was launched into the safety catch fence mounted atop the outside guardwall."

Hildebrand and driver Pippa Mann were also injured. Neither is thought to have suffered life-threatening injuries.

The English-born Wheldon was 33. Before the race, he tweeted that it was a "Big day today, $5,000,000.00 at stake!!! Heading to the track." The last tweet on his page is the single word "Green!!!!"